12-month furnace filters

Q. Are so-called 12-month furnace filters worth the cost? Do they really last that long, or is it more efficient and better to change the filter more frequently, using less-expensive filters?

A. If the touted 12-month filter fits into a standard 1-inch slot, it might not work effectively over time, said Bruce Boerner, an energy efficiency engineer at Xcel Energy.

"It will most likely get too dirty and the airflow will be reduced significantly over the 12 months," he said.

To be viable for 12 months, a filter would need to be 3 to 4 inches deep, he said.

"With the higher surface area, the filter would still be able to effectively remove the dirt and not have excessive reductions in airflow when the filter gets as dirty as it should when the filter is left in place for 12 months," Boemer said.

Using such a filter also would require duct modifications, he added.

Xcel also endorses following manufacturers' recommendations for a furnace, which generally call for checking the filter every month and changing it every three months.